This invention relates to a method and apparatus for protecting a money-handling unit, which is vulnerable to liquid attack. Although it is not limited to the following, the invention is particularly suitable for protecting coin-validating or coin-dispensing units used, for example, in gaming machines or vending machines.
It is a known problem that vandals sometimes inject liquid into the entryway of money-operated machines in an attempt to generate false electrical signals to obtain free vend product, or a free game, or free coins.
This can be a particular problem when a multiplexed signal bus is used to carry information from sensors in the coin mechanism to a control circuit, such as in the arrangement described in WO-A-93/01568. False signals occurring on the bus could cause erroneous dispensing of change, or erroneous accumulation of credit, when none is appropriate. It is known to provide a sensor for detecting the presence of liquid, but such a sensor would need to be connected to the control circuit by at least one extra wire; if additional liquid sensors are used, this would further increase the number of inputs required for the control circuit, which defeats the advantage of using a single signal bus.
Another type of problem stems from the limited capability of conventional techniques for detecting, and for dealing with, liquid attack.
For example, U.S. Pat. No. 5,318,164 assigned to the current applicant, and U.S. Pat Nos. 4,264,000 and 5,377,804 describe systems for shutting down the supply of power to the coin-operated machine immediately on sensing a liquid. These systems remain latched of in a permanent manner until an engineer is able to service the machines and to reset the liquid-sensing system.
Such systems can provide reliable operation for protecting the electrical circuitry as well as preventing fraudulent operation. However, when an engineer attends a machine which has shut down automatically, if no permanent damage has occurred, there may be nothing in the machine that requires servicing or repair. In that case all that the engineer has to do is to perform the relatively simple task of resetting the liquid-sensing system, which in most cases is done by pressing a "reset" button. Since it is very expensive to call out an engineer to service a shut-down machine, this does not represent good value-for-money for the machine owner. Also, the engineer is unlikely to be able to attend immediately, and the machine may have to remain inoperable for some time, and therefore lose custom, even though there is nothing wrong with the machine.
Of course, the attendance of the servicing engineer is always required when such systems shut down because the owner of the machine will not generally have sufficient knowledge and experience to judge whether any permanent damage has occurred, or whether further damage or defrauding may result if operation of the machine is continued
When an engineer arrives to attend to a machine which has shut down as a result of detected liquid, he will normally have to perform a complete service to check all of the parts and circuitry, even if there is no damage. This is because, assuming that the liquid has dried out, the engineer might not know which type of liquid caused the shut-down, and he will have to proceed on the assumption that permanent damage may have occurred.
Reference is also made to Japanese patent applications published under Nos. 1-219587(A), 2-118795(A) and 1-250189(A) which describe sensor circuitry for shutting down a vending machine when liquid is detected.